The present invention relates to cooling systems for large dynamoelectric machines such as turbine generators, and more particularly to liquid-cooled conductors for such machines.
Large turbine generators are usually of the inner cooled, or direct cooled, construction in which a coolant fluid is circulated through duct means in the stator and rotor slots in direct thermal relation with the current-carrying conductors inside the ground insulation. This type of construction provides a very effective cooling system and has made it possible to greatly increase the maximum capacities obtainable in large generators without exceeding the permissible limits of physical size. Hydrogen is usually used as the coolant fluid in these machines but in the largest sizes a more efficient coolant such as water is preferably used, at least in the stator windings. A closed, recirculating coolant system is used for liquid-cooled stator windings in which the coolant liquid is circulated through the internal ducts of the winding and through an external cooler. Stranded conductors are normally used in these large machines, and when a liquid coolant is used in the stator windings, some or all of the strands are made hollow to serve as the coolant ducts. The ends of the winding conductors are enclosed by headers which communicate with the hollow strands and which are connected in the coolant system to direct the flow of water to or from the hollow strands. The headers are preferably part of a connector means for making both hydraulic and electrical connections to the conductors.
In this type of construction, the high-voltage ground wall insulation of the conductor has usually terminated a short distance away from the header at each end of the conductor. This was intended to permit any water which might leak from the header, such as between strands, to escape and prevent it from migrating along the length of the conductor within the insulation and possibly causing a failure. It has been found, however, that this region closely adjacent the header at each end of the conductor is the region of greatest strain during operation, and fatigue failures of the strands in this area have occurred because of the high strain and the undesirably large vibration that may occur.